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Recent issues and 18 months of experience have shown me that shared storage for a small (2-4 node) virtualisation cluster is hard.

It is still practical and possible to build a shared storage cluster using Solaris, rather than buying super experience appliance storage. But you must always spec at least two storage nodes, otherwise you lock yourself into a structure that can be difficult to change. That includes changes that involve upgrades.

Virtualisation technology has moved a long way in the last couple years. And while I’m still formulating a new approach, there are many more options for flexible micro virtualisation clusters.

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I’ve got a couple XenServer vms that I never migrated to ESX. Time and complexity got in the way. In fact one of the reasons why I dislike XenServer is that fact that way it ran disk images was not portable. Where as with ESX and KVM I can migrate disk images between the two hypervisors without needing to chance anything in the guest. With XenServer at the time this was not easy. XenOSS has a similar issue with PV domains, although with KVM+xenner is meant to be able to run these.

Anyway here are a few links for converting disk images between formats.

I found though in the end that kvm-img or qemu-img has able to handle all the images I use: VHD, VMDK, RAW, and QCOW2. For example kvm-image convert disk.vhd -O raw disk.raw will work.

This leads to the nicest thing I found about KVM. With either ESXi 3.5 or vSphere 4 ubuntu 8.04 or 8.10 VMDK files I was able to: kvm-img convert -O raw disk.vmdk disk.raw. Then run this new disk in raw formatwith KVM plus virtio drivers and do so without any changes in the guest.